Modern semiconductor fabrication facilities (known as “fabs”) use tools that can process multiple wafers. The wafers are typically delivered to a tool from a stocker in a front opening unified pod (FOUP). The FOUPS may be hand carried to and from the tool or they may be delivered by an automated material handling system (AHMS) or overhead track (OHT) system. Wafers are transferred from the FOUPs to the tool through an equipment front end module (EFEM). The EFEM typically includes one or more load ports (LPs) and robot arm that takes the wafers from a FOUP at a given load port and delivers them to the tool. Initially, EFEMs had only one LP and the robot could handle the wafer with a very simple motion, in some cases, just a simple linear motion of the robot arm. Later EFEMs had two, then three, then four LPs arranged side by side horizontally. The side by side arrangement of the LPs required a complex motion of the robot arm in order to handle wafers at each LP. A simple combination of rotation about a vertical axis and translation perpendicular to the axis (sometimes referred to as R-theta motion) is not sufficient.
For example, FIG. 13A shows a typical R-theta robot 1300 having a mechanical arm mounted to a turntable 1302A. The mechanical arm includes a first link 1304A coupled to a second link 1306A by a motor 1308A. An end effector 1310A is coupled to the second link 1306A. Rotation of the turntable 1302A and the motor 1308A provides movement to the links 1304A, 1306A and end effector 1310A. A system of gears and pulleys restricts arm movement to three degrees of freedom: R (radial from center axis of the robot), theta (rotation) and (optionally) Z (translation along the center axis). The end effector 1310A is constrained by the mechanical system to always point away from the center axis of the turntable 1302A. If the LPs are arranged side-by-side, an extra degree of movement is required, in order to access the wafers orthogonal to the FOUP opening. The extra degree of movement can be supplied, e.g., by moving an R-theta robot along a track parallel to the front wall of the EFEM or by adding an extra degree of movement so that the end effector can move independent of the arm position.
For example, FIG. 13B shows a robot 1300B having a mechanical arm mounted to a turntable 1302B. The mechanical arm includes a first link 1304B coupled to a second link 1306B by a first motor 1308A. An end effector 1310B is coupled to the second link 1306B by a second motor 1309. Rotation of the turntable 1302B and the motors 1308B, 1309 provides independent movement to the links 1304B, 1306B and end effector 1310B. The robot 1300B has four degrees of freedom ?1, ?2, and ?3 and (optionally) Z. The links 1304B, 1306B and the end effector 1310B can move independently of each other and the end effector 1310B is free to point in any direction relative to the axis of the turntable 1302B. The extra degree of movement makes the robot complex in terms of both mechanical design and motion control hardware and software. This complexity can account for as much as 30% of the cost of an equipment front end module.
Thus, there is a need in the art, for an equipment front end module that overcomes the above disadvantages.